This invention relates to directly printable tapes, inks for printing upon said tapes, and a method for printing upon said tapes.
Adhesive tapes with printed indicia on the back side, i.e., the side opposite that bearing adhesive are useful for advertising and identification functions. As a practical matter, the adhesive is generally a pressure-sensitive adhesive. Inasmuch as pressure-sensitive adhesive tapes are those in which the adhesive has sufficient adhesion and tack to adhere to adherent surfaces with light finger pressure, the tapes are generally coated on the back side with a release agent. Such a coating permits the tape to be unwound easily in roll form without transfer of the adhesive to the back side of the tape. Thus, with printable pressure-sensitive adhesive tapes, the ink must adhere to the release coating, which is often called a "backsize", and not be removed by the adhesive in contact therewith.
Early attempts to provide printed pressure-sensitive adhesive tapes involved a process known as the "print seal process". In this process, the back side of the tape is printed with indicia, dried, and immediately overprinted with a release agent and dried before the adhesive surface contacts the printed indicia. Although this process produces a satisfactory tape when properly carried out, it requires a special printing machine with at least two printing and drying operations, making it inconvenient, expensive, and frequently variable in result.
A number of attempts have been made to provide printable, pressure-sensitive adhesive tapes which do not require overprinting. It has been particularly difficult to find a release agent capable of sufficiently retaining the printed indicia against the adhesive action of high performance or high adhesion adhesives, especially those based on block copolymer elastomers. Thus, it is desirable to provide a release coating composition which when employed with such block copolymer-based pressure-sensitive adhesives will impart to tapes the property of ready release and good printability without adversely affecting adhesion and tack of the adhesive. It is further desirable to provide a release coating composition capable of forming a coating which is resistant to splitting and to loss of desirable properties on aging.
Current packaging tapes are required to achieve a level of performance which imposes drastic constraints on those tapes, which must of necessity be printable and carry a sharp, clear imprinted message from the tape roll to the surface upon which the tape is to be applied. Commercial distribution of printable packaging tapes requires that the tape be shipped to a converter who applies the printed indicia, in turn selling the printed tape in dispensable roll form to the ultimate customer. At this stage, the tape may be subjected to reasonably lengthy periods of storage at conventional warehousing conditions including moderately elevated temperatures. During this time, the highly aggressive pressure-sensitive adhesive is in direct contact with the underlying printed surface, which may result in offsetting of the ink to the adhesive layer when the tape is ultimately dispensed from the roll.
The means for insuring sufficient anchorage of the printed matter to prevent this ink transfer, and the means for promoting satisfactory release of the adhesive layer from the backsize when the tape is in roll form are in essence diametrically opposed. Prior art attempts to balance these opposing forces have been accomplished only by cumbersome processing steps which complicate the production of such tapes and increase the expense thereof.
Attempts have also been made to modify commercially available inks for use with low adhesion backsize-coated pressure-sensitive adhesive tapes by the addition of natural or synthetic waxy materials, but such attempts have been unsatisfactory because such additives tend to migrate into the adhesive layer and cause a variety of deficiencies such as detackification and loss in adhesive and cohesive strength.